summaryrefslogtreecommitdiffstats
path: root/kernel/bpf/sockmap.c
blob: eef843c3b4193c238923f01802bd6baccbb614b8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
/* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 */

/* A BPF sock_map is used to store sock objects. This is primarly used
 * for doing socket redirect with BPF helper routines.
 *
 * A sock map may have BPF programs attached to it, currently a program
 * used to parse packets and a program to provide a verdict and redirect
 * decision on the packet are supported. Any programs attached to a sock
 * map are inherited by sock objects when they are added to the map. If
 * no BPF programs are attached the sock object may only be used for sock
 * redirect.
 *
 * A sock object may be in multiple maps, but can only inherit a single
 * parse or verdict program. If adding a sock object to a map would result
 * in having multiple parsing programs the update will return an EBUSY error.
 *
 * For reference this program is similar to devmap used in XDP context
 * reviewing these together may be useful. For an example please review
 * ./samples/bpf/sockmap/.
 */
#include <linux/bpf.h>
#include <net/sock.h>
#include <linux/filter.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/kernel.h>
#include <linux/net.h>
#include <linux/skbuff.h>
#include <linux/workqueue.h>
#include <linux/list.h>
#include <net/strparser.h>
#include <net/tcp.h>

#define SOCK_CREATE_FLAG_MASK \
	(BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)

struct bpf_stab {
	struct bpf_map map;
	struct sock **sock_map;
	struct bpf_prog *bpf_parse;
	struct bpf_prog *bpf_verdict;
};

enum smap_psock_state {
	SMAP_TX_RUNNING,
};

struct smap_psock_map_entry {
	struct list_head list;
	struct sock **entry;
};

struct smap_psock {
	struct rcu_head	rcu;
	/* refcnt is used inside sk_callback_lock */
	u32 refcnt;

	/* datapath variables */
	struct sk_buff_head rxqueue;
	bool strp_enabled;

	/* datapath error path cache across tx work invocations */
	int save_rem;
	int save_off;
	struct sk_buff *save_skb;

	struct strparser strp;
	struct bpf_prog *bpf_parse;
	struct bpf_prog *bpf_verdict;
	struct list_head maps;

	/* Back reference used when sock callback trigger sockmap operations */
	struct sock *sock;
	unsigned long state;

	struct work_struct tx_work;
	struct work_struct gc_work;

	void (*save_data_ready)(struct sock *sk);
	void (*save_write_space)(struct sock *sk);
	void (*save_state_change)(struct sock *sk);
};

static inline struct smap_psock *smap_psock_sk(const struct sock *sk)
{
	return rcu_dereference_sk_user_data(sk);
}

static int smap_verdict_func(struct smap_psock *psock, struct sk_buff *skb)
{
	struct bpf_prog *prog = READ_ONCE(psock->bpf_verdict);
	int rc;

	if (unlikely(!prog))
		return SK_DROP;

	skb_orphan(skb);
	/* We need to ensure that BPF metadata for maps is also cleared
	 * when we orphan the skb so that we don't have the possibility
	 * to reference a stale map.
	 */
	TCP_SKB_CB(skb)->bpf.map = NULL;
	skb->sk = psock->sock;
	bpf_compute_data_pointers(skb);
	preempt_disable();
	rc = (*prog->bpf_func)(skb, prog->insnsi);
	preempt_enable();
	skb->sk = NULL;

	return rc;
}

static void smap_do_verdict(struct smap_psock *psock, struct sk_buff *skb)
{
	struct sock *sk;
	int rc;

	rc = smap_verdict_func(psock, skb);
	switch (rc) {
	case SK_REDIRECT:
		sk = do_sk_redirect_map(skb);
		if (likely(sk)) {
			struct smap_psock *peer = smap_psock_sk(sk);

			if (likely(peer &&
				   test_bit(SMAP_TX_RUNNING, &peer->state) &&
				   !sock_flag(sk, SOCK_DEAD) &&
				   sock_writeable(sk))) {
				skb_set_owner_w(skb, sk);
				skb_queue_tail(&peer->rxqueue, skb);
				schedule_work(&peer->tx_work);
				break;
			}
		}
	/* Fall through and free skb otherwise */
	case SK_DROP:
	default:
		kfree_skb(skb);
	}
}

static void smap_report_sk_error(struct smap_psock *psock, int err)
{
	struct sock *sk = psock->sock;

	sk->sk_err = err;
	sk->sk_error_report(sk);
}

static void smap_release_sock(struct smap_psock *psock, struct sock *sock);

/* Called with lock_sock(sk) held */
static void smap_state_change(struct sock *sk)
{
	struct smap_psock_map_entry *e, *tmp;
	struct smap_psock *psock;
	struct socket_wq *wq;
	struct sock *osk;

	rcu_read_lock();

	/* Allowing transitions into an established syn_recv states allows
	 * for early binding sockets to a smap object before the connection
	 * is established.
	 */
	switch (sk->sk_state) {
	case TCP_SYN_SENT:
	case TCP_SYN_RECV:
	case TCP_ESTABLISHED:
		break;
	case TCP_CLOSE_WAIT:
	case TCP_CLOSING:
	case TCP_LAST_ACK:
	case TCP_FIN_WAIT1:
	case TCP_FIN_WAIT2:
	case TCP_LISTEN:
		break;
	case TCP_CLOSE:
		/* Only release if the map entry is in fact the sock in
		 * question. There is a case where the operator deletes
		 * the sock from the map, but the TCP sock is closed before
		 * the psock is detached. Use cmpxchg to verify correct
		 * sock is removed.
		 */
		psock = smap_psock_sk(sk);
		if (unlikely(!psock))
			break;
		write_lock_bh(&sk->sk_callback_lock);
		list_for_each_entry_safe(e, tmp, &psock->maps, list) {
			osk = cmpxchg(e->entry, sk, NULL);
			if (osk == sk) {
				list_del(&e->list);
				smap_release_sock(psock, sk);
			}
		}
		write_unlock_bh(&sk->sk_callback_lock);
		break;
	default:
		psock = smap_psock_sk(sk);
		if (unlikely(!psock))
			break;
		smap_report_sk_error(psock, EPIPE);
		break;
	}

	wq = rcu_dereference(sk->sk_wq);
	if (skwq_has_sleeper(wq))
		wake_up_interruptible_all(&wq->wait);
	rcu_read_unlock();
}

static void smap_read_sock_strparser(struct strparser *strp,
				     struct sk_buff *skb)
{
	struct smap_psock *psock;

	rcu_read_lock();
	psock = container_of(strp, struct smap_psock, strp);
	smap_do_verdict(psock, skb);
	rcu_read_unlock();
}

/* Called with lock held on socket */
static void smap_data_ready(struct sock *sk)
{
	struct smap_psock *psock;

	rcu_read_lock();
	psock = smap_psock_sk(sk);
	if (likely(psock)) {
		write_lock_bh(&sk->sk_callback_lock);
		strp_data_ready(&psock->strp);
		write_unlock_bh(&sk->sk_callback_lock);
	}
	rcu_read_unlock();
}

static void smap_tx_work(struct work_struct *w)
{
	struct smap_psock *psock;
	struct sk_buff *skb;
	int rem, off, n;

	psock = container_of(w, struct smap_psock, tx_work);

	/* lock sock to avoid losing sk_socket at some point during loop */
	lock_sock(psock->sock);
	if (psock->save_skb) {
		skb = psock->save_skb;
		rem = psock->save_rem;
		off = psock->save_off;
		psock->save_skb = NULL;
		goto start;
	}

	while ((skb = skb_dequeue(&psock->rxqueue))) {
		rem = skb->len;
		off = 0;
start:
		do {
			if (likely(psock->sock->sk_socket))
				n = skb_send_sock_locked(psock->sock,
							 skb, off, rem);
			else
				n = -EINVAL;
			if (n <= 0) {
				if (n == -EAGAIN) {
					/* Retry when space is available */
					psock->save_skb = skb;
					psock->save_rem = rem;
					psock->save_off = off;
					goto out;
				}
				/* Hard errors break pipe and stop xmit */
				smap_report_sk_error(psock, n ? -n : EPIPE);
				clear_bit(SMAP_TX_RUNNING, &psock->state);
				kfree_skb(skb);
				goto out;
			}
			rem -= n;
			off += n;
		} while (rem);
		kfree_skb(skb);
	}
out:
	release_sock(psock->sock);
}

static void smap_write_space(struct sock *sk)
{
	struct smap_psock *psock;

	rcu_read_lock();
	psock = smap_psock_sk(sk);
	if (likely(psock && test_bit(SMAP_TX_RUNNING, &psock->state)))
		schedule_work(&psock->tx_work);
	rcu_read_unlock();
}

static void smap_stop_sock(struct smap_psock *psock, struct sock *sk)
{
	if (!psock->strp_enabled)
		return;
	sk->sk_data_ready = psock->save_data_ready;
	sk->sk_write_space = psock->save_write_space;
	sk->sk_state_change = psock->save_state_change;
	psock->save_data_ready = NULL;
	psock->save_write_space = NULL;
	psock->save_state_change = NULL;
	strp_stop(&psock->strp);
	psock->strp_enabled = false;
}

static void smap_destroy_psock(struct rcu_head *rcu)
{
	struct smap_psock *psock = container_of(rcu,
						  struct smap_psock, rcu);

	/* Now that a grace period has passed there is no longer
	 * any reference to this sock in the sockmap so we can
	 * destroy the psock, strparser, and bpf programs. But,
	 * because we use workqueue sync operations we can not
	 * do it in rcu context
	 */
	schedule_work(&psock->gc_work);
}

static void smap_release_sock(struct smap_psock *psock, struct sock *sock)
{
	psock->refcnt--;
	if (psock->refcnt)
		return;

	smap_stop_sock(psock, sock);
	clear_bit(SMAP_TX_RUNNING, &psock->state);
	rcu_assign_sk_user_data(sock, NULL);
	call_rcu_sched(&psock->rcu, smap_destroy_psock);
}

static int smap_parse_func_strparser(struct strparser *strp,
				       struct sk_buff *skb)
{
	struct smap_psock *psock;
	struct bpf_prog *prog;
	int rc;

	rcu_read_lock();
	psock = container_of(strp, struct smap_psock, strp);
	prog = READ_ONCE(psock->bpf_parse);

	if (unlikely(!prog)) {
		rcu_read_unlock();
		return skb->len;
	}

	/* Attach socket for bpf program to use if needed we can do this
	 * because strparser clones the skb before handing it to a upper
	 * layer, meaning skb_orphan has been called. We NULL sk on the
	 * way out to ensure we don't trigger a BUG_ON in skb/sk operations
	 * later and because we are not charging the memory of this skb to
	 * any socket yet.
	 */
	skb->sk = psock->sock;
	bpf_compute_data_pointers(skb);
	rc = (*prog->bpf_func)(skb, prog->insnsi);
	skb->sk = NULL;
	rcu_read_unlock();
	return rc;
}


static int smap_read_sock_done(struct strparser *strp, int err)
{
	return err;
}

static int smap_init_sock(struct smap_psock *psock,
			  struct sock *sk)
{
	static const struct strp_callbacks cb = {
		.rcv_msg = smap_read_sock_strparser,
		.parse_msg = smap_parse_func_strparser,
		.read_sock_done = smap_read_sock_done,
	};

	return strp_init(&psock->strp, sk, &cb);
}

static void smap_init_progs(struct smap_psock *psock,
			    struct bpf_stab *stab,
			    struct bpf_prog *verdict,
			    struct bpf_prog *parse)
{
	struct bpf_prog *orig_parse, *orig_verdict;

	orig_parse = xchg(&psock->bpf_parse, parse);
	orig_verdict = xchg(&psock->bpf_verdict, verdict);

	if (orig_verdict)
		bpf_prog_put(orig_verdict);
	if (orig_parse)
		bpf_prog_put(orig_parse);
}

static void smap_start_sock(struct smap_psock *psock, struct sock *sk)
{
	if (sk->sk_data_ready == smap_data_ready)
		return;
	psock->save_data_ready = sk->sk_data_ready;
	psock->save_write_space = sk->sk_write_space;
	psock->save_state_change = sk->sk_state_change;
	sk->sk_data_ready = smap_data_ready;
	sk->sk_write_space = smap_write_space;
	sk->sk_state_change = smap_state_change;
	psock->strp_enabled = true;
}

static void sock_map_remove_complete(struct bpf_stab *stab)
{
	bpf_map_area_free(stab->sock_map);
	kfree(stab);
}

static void smap_gc_work(struct work_struct *w)
{
	struct smap_psock_map_entry *e, *tmp;
	struct smap_psock *psock;

	psock = container_of(w, struct smap_psock, gc_work);

	/* no callback lock needed because we already detached sockmap ops */
	if (psock->strp_enabled)
		strp_done(&psock->strp);

	cancel_work_sync(&psock->tx_work);
	__skb_queue_purge(&psock->rxqueue);

	/* At this point all strparser and xmit work must be complete */
	if (psock->bpf_parse)
		bpf_prog_put(psock->bpf_parse);
	if (psock->bpf_verdict)
		bpf_prog_put(psock->bpf_verdict);

	list_for_each_entry_safe(e, tmp, &psock->maps, list) {
		list_del(&e->list);
		kfree(e);
	}

	sock_put(psock->sock);
	kfree(psock);
}

static struct smap_psock *smap_init_psock(struct sock *sock,
					  struct bpf_stab *stab)
{
	struct smap_psock *psock;

	psock = kzalloc_node(sizeof(struct smap_psock),
			     GFP_ATOMIC | __GFP_NOWARN,
			     stab->map.numa_node);
	if (!psock)
		return ERR_PTR(-ENOMEM);

	psock->sock = sock;
	skb_queue_head_init(&psock->rxqueue);
	INIT_WORK(&psock->tx_work, smap_tx_work);
	INIT_WORK(&psock->gc_work, smap_gc_work);
	INIT_LIST_HEAD(&psock->maps);
	psock->refcnt = 1;

	rcu_assign_sk_user_data(sock, psock);
	sock_hold(sock);
	return psock;
}

static struct bpf_map *sock_map_alloc(union bpf_attr *attr)
{
	struct bpf_stab *stab;
	int err = -EINVAL;
	u64 cost;

	if (!capable(CAP_NET_ADMIN))
		return ERR_PTR(-EPERM);

	/* check sanity of attributes */
	if (attr->max_entries == 0 || attr->key_size != 4 ||
	    attr->value_size != 4 || attr->map_flags & ~SOCK_CREATE_FLAG_MASK)
		return ERR_PTR(-EINVAL);

	if (attr->value_size > KMALLOC_MAX_SIZE)
		return ERR_PTR(-E2BIG);

	stab = kzalloc(sizeof(*stab), GFP_USER);
	if (!stab)
		return ERR_PTR(-ENOMEM);

	/* mandatory map attributes */
	stab->map.map_type = attr->map_type;
	stab->map.key_size = attr->key_size;
	stab->map.value_size = attr->value_size;
	stab->map.max_entries = attr->max_entries;
	stab->map.map_flags = attr->map_flags;
	stab->map.numa_node = bpf_map_attr_numa_node(attr);

	/* make sure page count doesn't overflow */
	cost = (u64) stab->map.max_entries * sizeof(struct sock *);
	if (cost >= U32_MAX - PAGE_SIZE)
		goto free_stab;

	stab->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;

	/* if map size is larger than memlock limit, reject it early */
	err = bpf_map_precharge_memlock(stab->map.pages);
	if (err)
		goto free_stab;

	err = -ENOMEM;
	stab->sock_map = bpf_map_area_alloc(stab->map.max_entries *
					    sizeof(struct sock *),
					    stab->map.numa_node);
	if (!stab->sock_map)
		goto free_stab;

	return &stab->map;
free_stab:
	kfree(stab);
	return ERR_PTR(err);
}

static void smap_list_remove(struct smap_psock *psock, struct sock **entry)
{
	struct smap_psock_map_entry *e, *tmp;

	list_for_each_entry_safe(e, tmp, &psock->maps, list) {
		if (e->entry == entry) {
			list_del(&e->list);
			break;
		}
	}
}

static void sock_map_free(struct bpf_map *map)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
	int i;

	synchronize_rcu();

	/* At this point no update, lookup or delete operations can happen.
	 * However, be aware we can still get a socket state event updates,
	 * and data ready callabacks that reference the psock from sk_user_data
	 * Also psock worker threads are still in-flight. So smap_release_sock
	 * will only free the psock after cancel_sync on the worker threads
	 * and a grace period expire to ensure psock is really safe to remove.
	 */
	rcu_read_lock();
	for (i = 0; i < stab->map.max_entries; i++) {
		struct smap_psock *psock;
		struct sock *sock;

		sock = xchg(&stab->sock_map[i], NULL);
		if (!sock)
			continue;

		write_lock_bh(&sock->sk_callback_lock);
		psock = smap_psock_sk(sock);
		smap_list_remove(psock, &stab->sock_map[i]);
		smap_release_sock(psock, sock);
		write_unlock_bh(&sock->sk_callback_lock);
	}
	rcu_read_unlock();

	if (stab->bpf_verdict)
		bpf_prog_put(stab->bpf_verdict);
	if (stab->bpf_parse)
		bpf_prog_put(stab->bpf_parse);

	sock_map_remove_complete(stab);
}

static int sock_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
	u32 i = key ? *(u32 *)key : U32_MAX;
	u32 *next = (u32 *)next_key;

	if (i >= stab->map.max_entries) {
		*next = 0;
		return 0;
	}

	if (i == stab->map.max_entries - 1)
		return -ENOENT;

	*next = i + 1;
	return 0;
}

struct sock  *__sock_map_lookup_elem(struct bpf_map *map, u32 key)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);

	if (key >= map->max_entries)
		return NULL;

	return READ_ONCE(stab->sock_map[key]);
}

static int sock_map_delete_elem(struct bpf_map *map, void *key)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
	struct smap_psock *psock;
	int k = *(u32 *)key;
	struct sock *sock;

	if (k >= map->max_entries)
		return -EINVAL;

	sock = xchg(&stab->sock_map[k], NULL);
	if (!sock)
		return -EINVAL;

	write_lock_bh(&sock->sk_callback_lock);
	psock = smap_psock_sk(sock);
	if (!psock)
		goto out;

	if (psock->bpf_parse)
		smap_stop_sock(psock, sock);
	smap_list_remove(psock, &stab->sock_map[k]);
	smap_release_sock(psock, sock);
out:
	write_unlock_bh(&sock->sk_callback_lock);
	return 0;
}

/* Locking notes: Concurrent updates, deletes, and lookups are allowed and are
 * done inside rcu critical sections. This ensures on updates that the psock
 * will not be released via smap_release_sock() until concurrent updates/deletes
 * complete. All operations operate on sock_map using cmpxchg and xchg
 * operations to ensure we do not get stale references. Any reads into the
 * map must be done with READ_ONCE() because of this.
 *
 * A psock is destroyed via call_rcu and after any worker threads are cancelled
 * and syncd so we are certain all references from the update/lookup/delete
 * operations as well as references in the data path are no longer in use.
 *
 * Psocks may exist in multiple maps, but only a single set of parse/verdict
 * programs may be inherited from the maps it belongs to. A reference count
 * is kept with the total number of references to the psock from all maps. The
 * psock will not be released until this reaches zero. The psock and sock
 * user data data use the sk_callback_lock to protect critical data structures
 * from concurrent access. This allows us to avoid two updates from modifying
 * the user data in sock and the lock is required anyways for modifying
 * callbacks, we simply increase its scope slightly.
 *
 * Rules to follow,
 *  - psock must always be read inside RCU critical section
 *  - sk_user_data must only be modified inside sk_callback_lock and read
 *    inside RCU critical section.
 *  - psock->maps list must only be read & modified inside sk_callback_lock
 *  - sock_map must use READ_ONCE and (cmp)xchg operations
 *  - BPF verdict/parse programs must use READ_ONCE and xchg operations
 */
static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops,
				    struct bpf_map *map,
				    void *key, u64 flags)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
	struct smap_psock_map_entry *e = NULL;
	struct bpf_prog *verdict, *parse;
	struct sock *osock, *sock;
	struct smap_psock *psock;
	u32 i = *(u32 *)key;
	int err;

	if (unlikely(flags > BPF_EXIST))
		return -EINVAL;

	if (unlikely(i >= stab->map.max_entries))
		return -E2BIG;

	sock = READ_ONCE(stab->sock_map[i]);
	if (flags == BPF_EXIST && !sock)
		return -ENOENT;
	else if (flags == BPF_NOEXIST && sock)
		return -EEXIST;

	sock = skops->sk;

	/* 1. If sock map has BPF programs those will be inherited by the
	 * sock being added. If the sock is already attached to BPF programs
	 * this results in an error.
	 */
	verdict = READ_ONCE(stab->bpf_verdict);
	parse = READ_ONCE(stab->bpf_parse);

	if (parse && verdict) {
		/* bpf prog refcnt may be zero if a concurrent attach operation
		 * removes the program after the above READ_ONCE() but before
		 * we increment the refcnt. If this is the case abort with an
		 * error.
		 */
		verdict = bpf_prog_inc_not_zero(stab->bpf_verdict);
		if (IS_ERR(verdict))
			return PTR_ERR(verdict);

		parse = bpf_prog_inc_not_zero(stab->bpf_parse);
		if (IS_ERR(parse)) {
			bpf_prog_put(verdict);
			return PTR_ERR(parse);
		}
	}

	write_lock_bh(&sock->sk_callback_lock);
	psock = smap_psock_sk(sock);

	/* 2. Do not allow inheriting programs if psock exists and has
	 * already inherited programs. This would create confusion on
	 * which parser/verdict program is running. If no psock exists
	 * create one. Inside sk_callback_lock to ensure concurrent create
	 * doesn't update user data.
	 */
	if (psock) {
		if (READ_ONCE(psock->bpf_parse) && parse) {
			err = -EBUSY;
			goto out_progs;
		}
		psock->refcnt++;
	} else {
		psock = smap_init_psock(sock, stab);
		if (IS_ERR(psock)) {
			err = PTR_ERR(psock);
			goto out_progs;
		}

		set_bit(SMAP_TX_RUNNING, &psock->state);
	}

	e = kzalloc(sizeof(*e), GFP_ATOMIC | __GFP_NOWARN);
	if (!e) {
		err = -ENOMEM;
		goto out_progs;
	}
	e->entry = &stab->sock_map[i];

	/* 3. At this point we have a reference to a valid psock that is
	 * running. Attach any BPF programs needed.
	 */
	if (parse && verdict && !psock->strp_enabled) {
		err = smap_init_sock(psock, sock);
		if (err)
			goto out_free;
		smap_init_progs(psock, stab, verdict, parse);
		smap_start_sock(psock, sock);
	}

	/* 4. Place psock in sockmap for use and stop any programs on
	 * the old sock assuming its not the same sock we are replacing
	 * it with. Because we can only have a single set of programs if
	 * old_sock has a strp we can stop it.
	 */
	list_add_tail(&e->list, &psock->maps);
	write_unlock_bh(&sock->sk_callback_lock);

	osock = xchg(&stab->sock_map[i], sock);
	if (osock) {
		struct smap_psock *opsock = smap_psock_sk(osock);

		write_lock_bh(&osock->sk_callback_lock);
		if (osock != sock && parse)
			smap_stop_sock(opsock, osock);
		smap_list_remove(opsock, &stab->sock_map[i]);
		smap_release_sock(opsock, osock);
		write_unlock_bh(&osock->sk_callback_lock);
	}
	return 0;
out_free:
	smap_release_sock(psock, sock);
out_progs:
	if (verdict)
		bpf_prog_put(verdict);
	if (parse)
		bpf_prog_put(parse);
	write_unlock_bh(&sock->sk_callback_lock);
	kfree(e);
	return err;
}

int sock_map_prog(struct bpf_map *map, struct bpf_prog *prog, u32 type)
{
	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
	struct bpf_prog *orig;

	if (unlikely(map->map_type != BPF_MAP_TYPE_SOCKMAP))
		return -EINVAL;

	switch (type) {
	case BPF_SK_SKB_STREAM_PARSER:
		orig = xchg(&stab->bpf_parse, prog);
		break;
	case BPF_SK_SKB_STREAM_VERDICT:
		orig = xchg(&stab->bpf_verdict, prog);
		break;
	default:
		return -EOPNOTSUPP;
	}

	if (orig)
		bpf_prog_put(orig);

	return 0;
}

static void *sock_map_lookup(struct bpf_map *map, void *key)
{
	return NULL;
}

static int sock_map_update_elem(struct bpf_map *map,
				void *key, void *value, u64 flags)
{
	struct bpf_sock_ops_kern skops;
	u32 fd = *(u32 *)value;
	struct socket *socket;
	int err;

	socket = sockfd_lookup(fd, &err);
	if (!socket)
		return err;

	skops.sk = socket->sk;
	if (!skops.sk) {
		fput(socket->file);
		return -EINVAL;
	}

	if (skops.sk->sk_type != SOCK_STREAM ||
	    skops.sk->sk_protocol != IPPROTO_TCP) {
		fput(socket->file);
		return -EOPNOTSUPP;
	}

	err = sock_map_ctx_update_elem(&skops, map, key, flags);
	fput(socket->file);
	return err;
}

const struct bpf_map_ops sock_map_ops = {
	.map_alloc = sock_map_alloc,
	.map_free = sock_map_free,
	.map_lookup_elem = sock_map_lookup,
	.map_get_next_key = sock_map_get_next_key,
	.map_update_elem = sock_map_update_elem,
	.map_delete_elem = sock_map_delete_elem,
};

BPF_CALL_4(bpf_sock_map_update, struct bpf_sock_ops_kern *, bpf_sock,
	   struct bpf_map *, map, void *, key, u64, flags)
{
	WARN_ON_ONCE(!rcu_read_lock_held());
	return sock_map_ctx_update_elem(bpf_sock, map, key, flags);
}

const struct bpf_func_proto bpf_sock_map_update_proto = {
	.func		= bpf_sock_map_update,
	.gpl_only	= false,
	.pkt_access	= true,
	.ret_type	= RET_INTEGER,
	.arg1_type	= ARG_PTR_TO_CTX,
	.arg2_type	= ARG_CONST_MAP_PTR,
	.arg3_type	= ARG_PTR_TO_MAP_KEY,
	.arg4_type	= ARG_ANYTHING,
};